Among theories which ﬁt all of our data, we prefer the simpler over the more complex. Why? Surely not merely for practical convenience or aesthetic pleasure. But how could we be justiﬁed in this preference without knowing in advance that the world is more likely to be simple than complex? And isn’t this a rather extravagant a priori assumption to make? I want to suggest some steps we can take toward reducing this embarrassment, by showing that the assumption which supports favouring simplicity is far more modest than it ﬁrst seems